Structural truss construction with membrane coverings

ABSTRACT

A structural truss has upper and lower wooden chords separated along their lengths by vertical wooden struts. The chords and struts are joined together to form the truss frame solely by adhesive-backed paper membranes covering the opposite sides of the frame so as to transmit tensile stresses within the frame. The truss may be manufactured in multiples of various lengths by a continuous assembly line process.

United States Patent [1 1 Shannon et al. 4 Nov. 6, 1973 [54] STRUCTURALTRUSS CONSTRUCTION 3,470,661 10/1969 Johnson 52/642 WITH MEMBRANECOVERINGS 3,039,152 6/1962 Hillesheim 52/642 92,205 7/1969 Mullett52/629 [76] Invent rs: MI ha J. a n 130 Greenwood 3,079,649 3/1963Willatts 52 731 Ave., Bend, Oreg. 97701; George C. Sheldon, 3033 NW.Quimby St. FOREIGN PATENTS OR APPLICATIONS Portland, 0 2 0 818,3548/1959 Great Britain 52/629 Filed! All 1971 Primary Examiner-Henry C.Sutherland [211 App]. No; 171,214 Assistant Examiner-Leslie A. Br'aunAttorney-Stephen W. Blore, Kenneth S. Klarqulst, .loseph B. Sparkman,James Campbell, Jr., James S. [52] US. Cl. 52/634, 52/515, 52/638 LeighJohn Hall Arthur whinston and J h p [51] Int. Cl. E04c 3/14, E040 3/29Dene [58] Field of Search 52/634, 636, 638,

2/ 2 1 515 57 ABSTRACT A structural truss has upper and lower woodenchords [5 6] References cued separated along their lengths by verticalwooden struts. UNITED STATES PATENTS The chords and struts are joinedtogether to form the 3,545,155 12/1970 Church 52/515 truss frame solelyby adhesive-backed paper mem' 2, 11 n 52/613 branes covering theopposite sides of the frame so as to 513710 1394 ''Y---- 52/612 transmittensile stresses within the frame. The truss 2::2 may be manufactured inmultiples of various lengths by c enzie v 2,375,910 5,1945 a continuousassembly line process. 2,230,628 2/1941 1 Claim, 4 Drawing FiguresSHANNON C. SHELDON INVENTORS.

MICHAEL J.

GEORGE Patented Nov. 6, 1973 BUCKHORN, BLORE, KLARQUIST & SPARKMANATTORNEYS STRUCTURAL TRUSS CONSTRUCTION WITH MEMBRANE COVERINGSBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to structural trusses and a method of manufacturingthe same.

2. Description of the Prior Art Conventional wooden structural trusses,such as roof and floor trusses used in the building industry, are madeof long upper and lower wooden chords separated by a combination ofvertical and diagonal wooden struts'joined to the chords by nails ormetal truss connector plates. Such conventional trusses are relativelyheavy because of the large number of wooden struts they contain and alsobecause of the large amount of metal in them, particularly when trussconnector plates are used. They are also expensive be cause each suchtruss is custom made, either at the job site or at a nearby factory.Because of ever-rising building costs, there is a need for aninexpensive, lightweight, yet relatively strong structural trusssuitable for use in residential and light commercial buildingconstruction.

SUMMARY OF THE INVENTION The foregoing needs are met by the presentinvention which comprises a structural truss composed of the usual upperand lower chord members separated by upright struts. However, the trussof the invention is unique in that it does not contain the usual metalfasteners joining the struts and chords nor the usual diagonal struts.Instead, the chord and vertical strut truss frame described is coveredon both sides by continuous adhesive-backed paper membranes which arejoined to both the struts and the chords to hold such members inabutting relationship. Thus externalloads applied to the truss aretransmitted within the truss in tension primarily by the membranes,whereas compressive stresses within the truss are transmitted by thechords and vertical struts. The result is a structural truss which isreasonably strong, lightweight and inexpensive to manufacture, transportand erect. The membranes are made of paper of various tensile strengthsdepending on the need and are preferably treated for weather protectionand to retard deterioration.

The truss may be conveniently manufactured continuously in an assemblyline process by moving parallel chord lengths from a continuous fingerjointing machine along horizontal paths, applying one of theadhesive-backed membranes to one side of the chord lengths at a firststation, inserting the struts at intervals between the chord lengths andonto the membrane at a second station, applying the second membrane tothe opposite sides of the struts and chord lengths at a third station,then curing the adhesive-backed membranes to I join the structuralmembers into a relatively rigid truss frame at a fourth station, andfinally at a fifth station cuttingthe resultingcontinuous frame intosections of predetermined length.

Primary objects of the invention are to provide a structural truss whichis strong and durable, yet lightweight and inexpensive to manufacture,transport and install.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects, features andadvantages of the invention will become more apparent from the followingdetailed description which proceeds with reference to the accompanyingdrawing wherein:

FIG. 1 is a side elevation of a structural truss in accordance with theinvention with portions of both covering membranes removed for clarityof illustration;

FIG. 2 is a side elevational view on a smaller scale of a conventionalstructural truss of the prior art;

FIG. 3 is a vertical sectional view taken along the line 3-3 of FIG. 1on an enlarged scale; and

FIG. 4 is a schematic side elevational view illustrating a method orapparatus for manufacturing the truss of FIG. 1.

DETAILED DESCRIPTION With reference to the drawing, a conventional truss10 of the prior art is shown in FIG. 2 composed of an upper chord member12, a lower chord member 14, vertical struts 16, right diagonals l8 andleft diagonals 19. The various vertical and diagonal struts are joinedto the chords by metal truss connector plates 20. Such plates are wellknown in the art and usually consist of heavy-gauge sheet metal platesfrom which nail-like projections are punched, with the plate projectionsbeing pressed into the opposite sides of the wooden truss members at thevarious joints. As previously mentioned, wooden structural trusses ofthis type are heavy and expensive because of the large-scale use ofmetal connector plates and diagonal struts to transmit stresses, usuallyin tension, within the truss frame in reaction to external loads.

The foregoing prior art conventional truss construction should becompared with a structural truss 30 in accordance with the invention asshown in FIG. 1. The truss 30 is composed of an upper wooden chordmember 32, a lower wooden chord member 34, and vertical wooden strutmembers 36, but nodiagonals, unlike the prior art truss construction.Furthermore, vertical struts 36 are not joinedto the upper and lowerchords 32, 34 by metal connector plates, or in fact by any metalfasteners whatsoever. Instead, the truss frame of FIG. 1 is covered onits opposite sides by thin, flexible membranes 38, 39,prefe rably ofpaper or other cellulose fiber material of high tensile strength.

As shown in FIG. 3, each membrane 38, 39 has a heat curable adhesivebacking 40 which joins the membranes to the'opposite side surfaces ofthe chords and struts so that the membranes join the struts and chordstogether into a relatively rigid truss framework.

When the flexible membranes 38, 39 are made of paper, they arepreferably coated or impregnated with a protective material forweatherproofing and toretard deterioration with age. Papers or otherthin, flexiblemembrane material are selected according to tensilestrength to meet design considerations. The sizeof the various chord andstrut members are similarly selected. For most residential and lightcommercial building applications, the chord and strut members wouldusually be made from standard 2X4 dimension lumber. The membranes couldbe composed of a kraft-type paper of high tensile strength. In someapplications, 1X4 lumber would be suitable for the struts because of thehigh compressive strength of wood under column loading, which would bethe primary type of loading of such struts in the truss of theinvention.

Although a box truss is illustrated, pitch roof and other types oftrusses could also be manufactured in accordance with the invention.

In use, it is assumed that the truss will be loaded externally along thetop chord. Under this ideal condition and uniform loading, the chordsand struts will be in compression, with the membranes transmittingstresses in tension.

METHOD OF MANUFACTURE FIG. 4 illustrates a method of manufacturing thebox truss of FIG. 1 by a high-speed assembly line technique. A pair ofcontinuous chord lengths 50, 51 proceed horizontally along parallelpaths downstream from a continuous finger-jointing machine (not shown)which forms the continuous lengths. At a first station 52 a papermembrane 53 is applied to the underside of the chords by a pressure roll54 after an adhesive backing is sprayed onto the paper at 55 as it isunrolled from its supply roll 56.

The continuous membrane-backed chord lengths proceed from the firststation to a second station 58 where a magazine 59 inserts precut strutmembers 36 downwardly between the continuous chord lengths 50, S1 and ontop of the adhesive backing of membrane 53.

From second station 58 the membrane-backed chord lengths with spacedstruts therebetween proceed to a third station 60 where a secondpressure roll 61 applies the second membrane 62 to the upper faces ofthe chords and struts after an adhesive backing is sprayed onto themembrane at 63 as it is unrolled from its supply roll 64.

Thereafter the loosely assembled continuous truss frame proceeds to afourth, curing station 66 where a microwave or other suitable energysource 67 is used to cure the adhesive and thereby secure the membranesand other truss frame elements together.

From the curing station the now one-piece continuous frame proceeds to afifth, cutting station 68 where a knife 69 cuts the continuous trussframe into sections of predetermined length to form multiple box trussesready for use. A pair of end struts are placed side-byside between thechord lengths at points where the lengths are to be cut so that eachresulting truss is complete when cut.

The truss as described is' inexpensive as previously mentioned becauseof several factors. One of these factors is low material cost. The paperrequired for the truss is less expensive than the wood components itreplaces. Furthermore, standard 2X4s can be used for the compressionmembers of the truss. Additionally, glue replaces expensive metal platesor nails as the fastening agent.

A second factor is low production cost. Paper can be used moreefficiently than wood because a roll of paper having the exactdimensions necessary for a given truss can be used in feeding the papermembrane onto the truss frame in accordance with the method of theinvention. On the other hand, a relatively rigid material, such asplywood, if used as the skin or membrane would have to be cut from astandard 4X8 or other standard size sheet, resulting in much waste ofmaterial. Similar waste results from using'wood diagonal strut ,membersin a conventional truss.

A third cost factor is the low shipping and handling costs that result.The relatively light weight of the paper reinforced truss provides easyhandling in the shop and in the field, and reduces packaging andshipping costs. Such lightweight trusses should also require smaller,less expensive types of handling equipment or at least should be lessabusive to existing equipment.

A fourth cost factor is the efficient use of materials provided by thetruss and method of the present invention. Paper, which has a hightensile strength, is used as the principal tension component of thetruss. Thus there is less waste in that materials such as wood havinghigh tensile and compressive strengths are not used in applicationswhere only high tensile strength is required.

The paper reinforced truss described also has other advantages andfeatures not necessarily limited to cost as follows:

First, the paper reinforced truss provides structural designflexibility. The truss can be designed to fit the job. It does not haveto be overbuilt to apply to many different applications.

Second, the paper reinforced truss provides visual design flexibility aswell as structural flexibility. The shape of the truss can be changedwith the paper sheathing concept more easily than with conventionaltechniques.

Third, the paper membranes present unlimited graphic, color and texturepossibilities independent of structural considerations.

Fourth, a resin impregnation of the paper membranes would probably benecessary or at least desirable to provide resistance to moisture attackwhich could weaken the tensile strength of the membrane. Such resinimpregnation would also help prevent or at least retard degradation ofthe paper because of its sulfur content. It is believed that the sulfurcontent of paper reacts with atmospheric oxygen to cause ultimate paperfailure. The resin would serve as a shield in this regard. In any event,ultimate paper failure should occur only after a period of time whichwould greatly exceed the expected life of the building itself.

Although the paper reinforced truss of the invention has been describedfor use in building applications, such structural trusses on a smallerscale could also be used in lighter structural applications such asin'furniture construction.

Having illustrated and described what is presently apreferred'embodiment of the invention, it should be apparent to thoseskilled in the art that the same permits of modification in arrangementand detail. We claim as our invention all such modifications as comewithin the true spirit and scope of the following claims.

We claim:

l. A structural truss for use as a load-supporting and transmittingstructural building component supported in a vertical plane at itsopposite lower ends and freespanning a distance between said ends, saidtruss including an upper rigid wooden chord member defining the lengthdimension of said truss and adapted to receive vertically appliedexternal loads from above,

a lower rigid wooden chord member spaced vertically below said upperchord member and adapted to be supported from below at its opposite endsto receive at said ends vertically applied external reaction loads frombelow and to free-span a distance between said ends,

a plurality of rigid wooden strut compression members extendingvertically between said upper and and adhesive means affixing saidflexible tension membranes to the faces of said upper and lower chordsand to the faces of said strut compression members in a manner such thatsaid membranes provide the sole interconnection between said chordmembers and said strut members and such that said membranes resistexternal loads applied to said framework in tension,

said flexible tension membranes comprising weatherresistant paper sheetmaterial.

1. A structural truss for use as a load-supporting and transmittingstructural building component supported in a vertical plane at itsopposite lower ends and free-spanning a distance between said ends, saidtruss including an upper rigid wooden chord member defining the lengthdimension of said truss and adapted to receive vertically appliedexternal loads from above, a lower rigid wooden chord member spacedvertically below said upper chord member and adapted to be supportedfrom below at its opposite ends to receive at said ends verticallyapplied external reaction loads from below and to free-span a distancebetween said ends, a plurality of rigid wooden strut compression membersextending vertically between said upper and lower chord members atspaced intervals along the length of said chord members with theopposite ends of said strut compression members abutting inside edges ofsaid chord members at butt joints to define a structural framework, thelength dimension of said truss as defined by the length of said chordmembers being substantially greater than the height dimension of saidtruss as defined by the vertical distance between said chord members, apair of thin, flexible continuous tension membranes covering theopposite sides of said framework, and adhesive means affixing saidflexible tension membranes to the faces of said upper and lower chordsand to the faces of said strut compression members in a manner such thatsaid membranes provide the sole interconnection between said chordmembers and said strut members and such that said membranes resistexternal loads applied to said framework in tension, said flexibletension membranes comprising weather-resistant paper sheet material.